Soft hydrogel ophthalmic lenses, such as contact lenses, can be produced by polymerizing or curing a polymerizable lens precursor composition in a lens mold. Lens molds used in the molding of ophthalmic lenses, such as cast molding of contact lenses, typically comprise a first mold member and a second mold member. The first mold member and second mold member are put in contact with each other to form a lens shaped cavity containing the polymerizable lens precursor composition. The first mold member can be understood to be a female mold member or a mold member having a concave lens defining surface (e.g., a concave molding surface) that forms the front surface or anterior surface of the ophthalmic lens. The first mold member can also be understood to be a front curve mold member. The second mold member can be understood to be a male mold member or a mold member having a convex lens defining surface (e.g., a convex molding surface) that forms the back surface or posterior surface of the ophthalmic lens. The second mold member can also be understood to be a back curve mold member.
The first mold member and the second mold member can comprise a thermoplastic material that is capable of being injection molded. In other words, the first mold member and the second mold member can be produced by injection molding a thermoplastic material into mold member cavities. Examples of thermoplastic materials used to produce the first mold member and the second mold member include, without limitation, polypropylene materials, polystyrene materials, polyethylene materials, and materials comprising ethylene vinyl alcohol polymers or polyvinyl alcohol polymers.
The lens-defining surfaces of the first mold member and the second mold member are shaped by inserts provided or mounted in an injection molding machine or a component of an injection molding machine. These inserts are formed from metal materials, such as steel, brass, copper, chromium, cobalt-nickel, alloyed martensitic steel, and the like. The inserts are machined and include an optical quality surface that defines an optical surface or the lens-defining surface of an ophthalmic lens mold member. The optical quality surface of the inserts can be machined to provide a lens mold member having a molding surface effective to produce an ophthalmic lens with a desired optical power, and therefore, the inserts can be understood to be power inserts or optic power inserts. In other words, an optic power insert, as used herein, refers to an insert of an ophthalmic lens mold injection molding system that comprises a surface that forms a lens-defining surface of an ophthalmic lens mold. The optic power inserts can be one piece inserts or two-piece inserts. The optic power inserts of existing systems and methods are placed in bushings that have a smooth internal bore or an internal bore defined by a sidewall that has an uncorrugated surface or a curviplanar surface. As used herein, a curviplanar surface refers to a curved surface, such as an interior sidewall surface of a cylinder, that can be theoretically flattened onto a single plane. Conventional bushings accommodate the optic power inserts in the smooth internal bore in a sealed configuration.
Injection molding of ophthalmic lens mold members includes directing a molten thermoplastic material into a cavity that includes the optical quality surface of the optic power inserts. During the procedure, gases are released from the thermoplastic material. The released gases result in an increase in pressure within the mold cavity. As described in U.S. Publication No. 20030164565, some two piece steel injection mold inserts have a zero vent design that eliminates a vent. Other inserts and injection molding systems include one or more vents located on a plane that is orthogonal to the length or longitudinal axis of the insert. For example, U.S. Pat. No. 5,540,410 states vent holes are disposed at angles 20° to 30° off of a diameter of the concavo-convex mold portion defined by the thermoplastic injection point and the convergence point of the thermoplastic resin. U.S. Pat. Nos. 5,545,366; 5,702,735; and 5,861,114 describe the use of one ejector pin located at the opposite side of a hot runner gate to vent gas. However, when no vents are provided, or when one or more vents are provided as described above, gas pressure build-up still remains a problem. For example, the increased gas pressure can result in a tilting of the optic power insert or decentration of the optic power insert. Changes in the optic power insert position negatively affects the ophthalmic lens molds produced with the optic power inserts. For example, positional changes can alter the shape of the lens mold and thereby affect the power of the lens produced with the lens mold, affect a toric axis of the lens mold and the lens obtained therefrom, and can create bubbles in the lens mold which can affect the quality of the lenses obtained therefrom. The increased gas pressure over time results in a decrease of lens mold quality and lens mold quality consistency and therefore reduced ophthalmic lens quality and quality consistency, and further results in increased manufacturing time, effort, and costs.
In addition, residual components, such as volatile agents and the like, that are present in the gas can accumulate at or near the contact region of the optic power inserts and the curviplanar surface of the bushing. As the amount of residual components increases, the ability to remove the optic power inserts from the bushing becomes difficult leading to an increase in manufacturing time and increased costs and effort in the production of ophthalmic lens molds and molded ophthalmic lenses.
Thus, there remains a need for new devices, systems, and methods for injection molding ophthalmic lens molds with improved quality and quality consistency among ophthalmic lens molds and molded ophthalmic lenses obtained therefrom. In view of the above, it can be appreciated that an existing problem relates to improving the quality and quality consistency of injection molded ophthalmic lens molds and molded ophthalmic lenses obtained therefrom.